Complete/Fix/Standardize JavaDoc

1. Write JavaDoc comments for all class variables and functions.
2. In many cases, there are multi-line JavaDoc comments where the opening ```/**``` and closing ```*/``` could be moved onto the same line as the comment itself.
3. There are functions with unfinished JavaDoc comments.
4. JavaDoc comments on classes can be removed if they have no useful information (Ex. A one-line description of the class and author tag).